Taxonomy, chromosome numbers, clonal diversity and population dynamics of Phragmites australis

Phragmites australis (Cav.) Trin. ex Steud. (common reed) is one of the most widespread plant species in the world. The species has a high phenotypic variation in morphology and life-history traits. This high phenotypic variation can be related to variance in chromosome numbers, clonal diversity, plasticity of clones or a combination of these. An overview of our present, still limited, knowledge concerning the amounts, causes and maintenance of genetic diversity in P. australis is given. In P. australis a large range in euploid number has been found (between 3x-12x, except for 5x and 9x, with x=12). In Europe tetraploids are dominant, whereas octoploids predominate in Asia. Aneuploids also occur regularly in P. australis, and differences in chromosome numbers have been observed even within clones. Clonal diversity in P. australis has been studied using allozyme polymorphisms and molecular markers. Both mono- and polyclonal stands are known to exist. A surprisingly high number of clones has been found in European stands. Environmental and genetic factors, which may account for this high clonal diversity, are discussed. In most studies on the occurrence of ecotypes in P. australis no distinction has been made between plastic and genetic variation. But evidence exists that responses to climate, hydrology and salt have a genetic basis. Until now no attempts have been made to determine which genes or gene complexes are responsible for these different responses. (C) 1999 Elsevier Science B.V. All rights reserved.